Image digitizers provide a means to capture strokes made with a digital stylus on a digitizing surface. Particular digitizer models provide a capability to record hand written materials on a sheet of paper while simultaneously generating an electronic copy. Such digitizers conventionally employ a pen-tipped stylus and a sheet of paper. The paper is mounted over a digitizing surface which includes detectors for sensing the strokes or annotations made on the paper using the stylus.
A conventional image digitizer is shown in FIG. 1. As shown, the digitizer 10 is connected to a workstation 12. As notations are made on the paper 14 using the pen-tipped stylus 16, an electronic copy of the notation is captured and represented on the workstation monitor 18. At the conclusion of a recording session, i.e., once the paper is removed, the electronic copy is stored for later retrieval and reproduction.
Image digitizers have proven useful in capturing information recorded on a single piece of paper during a single writing session. However, conventional image digitizers lack the capability to recognize and distinguish a particular sheet of paper. Therefore, once a sheet of paper has been recorded and removed from the digitizer, the digitizer cannot recognize that the same sheet of paper has been remounted onto the digitizer. The inability of the digitizer to recognize a particular sheet of paper precludes retrieving a previously stored image which corresponds to the remounted sheet of paper. In the context of written examinations, for example, it is often necessary to remount prior sheets of paper that have already been written on and make additional annotations or corrections. Because conventional digitizers are incapable of identifying a previously recorded page, such conventional digitizers cannot be effectively used in many applications such as written examinations.
U.S. Pat. No. 5,243,149 (Comerford) discloses an apparatus for improving the paper interface to a computer system. In that system, a previously digitized image of a page of hand written text can be printed on a new page of paper. The system will also print, on the same page, a bar code which uniquely identifies the image to the system. Thereafter, if the printed image is loaded onto the digitizer, a scanner attached to the digitizer can be used to scan the bar code. The bar code signifies to the system that the printed page is one that is stored in the system and provides indexing information from which the image can be retrieved. The system retrieves the digital image and allows the operator to make annotations.
Thus, Comerford discloses a method of annotating a system generated copy of previously hand written material. Comerford does not disclose a means to annotate the same sheet of paper which was previously mounted on the digitizer. This distinction is an important one. It is not always practical to print a previously digitized image for the purpose of generating a bar code which can then be used by the system to identify the particular page. For example, in a written examination it is desirable to permit test takers to simply remount any sheet of paper so that corrections and other annotations may be made to text previously written on the same sheet of paper. Moreover, it is not feasible during a testing session to direct test takers to print out digital images and apply bar codes to those printed sheets before making corrections or annotations as would be required by a system such as that disclosed by Comerford.
Therefore, there exists a need for an image digitizer capable of automatically detecting a page identifier for a sheet of paper mounted thereon and further capable of recording all annotations and corrections in an electronic file associated with the sheet of paper on which the corrections and annotations are made.